Ask the average person to name a living fossil, the chances are they will think of the coelacanth, or perhaps horseshoe crabs. However, plant examples of living fossils are all around us, surviving from long before the rise of today’s dominant plants. The flowering plants, or angiosperms, are the basis of our food chain and include grasses and broad-leaved trees. But seed plants such as conifers and cycads, and even ancient spore producers such as ferns and clubmosses, continue to earn a living in environments where they are not squeezed out by highly efficient, flowering newcomers.

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One of the most well-known plant survivors is Ginkgo biloba – the only living species of its group, which is first recognised in the fossil record nearly 300 million years ago. By any given definition of “living fossil” – and there are many – Gingko biloba fits the bill. It is a long-lived, deciduous tree with distinctive fan-shaped leaves. Its common name is the maidenhair tree, and the etymology of this name doesn’t get discussed much. This is surprising given that, along with the maidenhair fern, which has similarly shaped leaves, they are the only species I know of that are named after a pubic triangle.

Ginkgo biloba is everywhere in the modern world, if you know where to look. It is highly tolerant of pollution, and so it is a favourite with city planners. It is also hugely significant in Japanese culture. Indeed, the renowned botanist Sir Peter Crane has written an entire book in praise of the Ginkgo which intertwines its cultural and scientific history. Extracts from Ginkgo leaves are also popular as a dietary supplement, taken to treat dementia and other disorders.

Hundreds of species of the genus Ginkgo are recognised from leaf fossils throughout the Mesozoic era, but quantifying its true diversity in the past is difficult. This comes down to a fundamental problem with studying fossil plants: you rarely find all of the organs of a plant preserved together. Reproductive structures such as cones and flowers are often key to identifying a plant, but in most cases they are simply not present. For most specimens of Ginkgo-like fossils, we only have leaves.

A glance in any autumn gutter will show you that most of the time, leaves readily decompose. However, in the right conditions, the waxy outer layer of a leaf, known as the cuticle, can be preserved in exquisite detail and bears the details of the epidermal cells it once coated. If we look at the preserved cuticle using a microscope, we can see an ancient leaf on a cellular scale. Some of the most beautiful examples can be found in the Jurassic rocks of the Yorkshire coast, where leaves called Ginkgoites huttoni can be found in sandstone slabs laid down in floodplains 170 million years ago. There’s even evidence for insect mimicry of Ginkgo leaves in the Jurassic.

Ginkgoites huttoni – an extinct gingko species fossilised from the Jurassic period, found in Iran. Photograph: Laboratory of Paleobotany/University of Jussieu

This is all fascinating and aesthetically pleasing – but (as we are increasingly asked by research funders) what good does studying these fossils do? These ancient survivors are actually very useful. Because preserved cuticles show us the leaf epidermal cells, we can see the arrangement and density of stomata. Stomata are the tiny pores in leaves that allow gaseous exchange. Plants also lose water vapour through these pores, and have sophisticated systems which dynamically control their opening and closing. Studying stomata in fossil cuticles can tell us a great deal about the atmosphere in the past, and how the atmosphere changes over geological time.

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In order to say sensible things about what fossil stomata tell us, we need some way of calibrating this data with a living equivalent. And sure enough, Ginkgo biloba has been grown in experimental conditions such as increased levels of carbon dioxide, and the leaves compared to fossils from geological periods thought to have different atmospheric carbon dioxide levels. Stomatal densities go down as carbon dioxide concentrations go up. Experimental work on Ginkgo and other living fossils such as Metasequoia glyptostroboides (dawn redwood) and Wollemia nobilis (the inaccurately named Wollemi pine) has built up a large body of evidence for species-specific responses to carbon dioxide concentrations.

Newer models of carbon dioxide concentration over the last half a billion years use a universal equation for leaf gas exchange for fossil leaves, and forego the need for a modern equivalent for each species. This doesn’t mean that living fossils such as Ginkgo are now redundant in this work, but rather we need to study a wider range of living fossils to make sure such models are accurate across more types of plant. This will only become more important as anthropogenic climate change pushes our atmosphere into uncharted territory (for humans, anyway).